Frequency changer set



June 23, 1942.

FREQUENCY CHANGER SET Filed April 1, 1942 W figl. lri f h f" a2Inventor: Charles C. Clymev",

His Attorney,

c. c. CLYMER 2,287,603

Patente d June 23, 1942 2,287,603 FREQUENCY CHANGER SET Charles C.Clymer, Altamont, N. Y., assignor to General Electric Company, acorporation of New York Application April 1, 1942, Serial No. 437,107

3 Claims.

My invention relates to frequency changer sets such as those employed toconnect two power systems of different fixed frequencies or to supplypower from a power system of fixed frequency to a system at a differentfrequency. My invention has for its purpose an economical use of themachines of the set and good power factor control while allowingflexibility as to the direction and extent of power flow through the setand to allow for slight variations in the frequency relation of the twointerconnected power systems.

The features of my invention which are believed to be novel andpatentable will be pointed out in the claims appended hereto. For abetter understanding of my invention reference is made in the followingdescription to the accompanying drawing illustrating in Fig. 1 myfrequency changer set as connected between two power systems ofdifferent frequency and Fig. 2 represents an automatic control featurethat may be used.

For the purpose of illustration in Fig. l, I have represented myfrequency changer set as connected between a 60 cycle power system Ii]and a 25 cycle power system II. The main machines of the set comprise awound secondary induction machine I2 and a synchronous machine I3directly connected together by shaft I I. The auxiliary or controlapparatus comprises a direct current machine I5 connected to shaft I4and driven with the main set and an auxiliary set consisting of asynchronous machine I6 directly connected to a direct current dynamoelectric machine I1.

When in operation as a frequency changer set the secondary winding ofmachine I2 is connected to the primary winding of synchronous machinethrough slip rings I8 and connections I9 and the armature windings ofthe direct current machines I5 and I! are connected in serice. Thedirect current field windings of the synchronous machines I3 and I6 andof the direct current machines I5 and I! are supplied from a directcurrent bus 20 the voltage of which is independent of the armaturevoltage of the direct current machines. The bus 20 may be supplied by adirect current exciter 2| directly connected with and driven by theauxiliary set as shown. The direct current field windings of thesynchronous machines I3 and I6 have rheostats 22 and 23 in theirenergizing circuits for power factor control purposes. The fieldwindings 24 and 25 of the direct current machines have rheostats 26 and21 in their energizing circuits to control the direction and magnitudeof i start the larger set using machine I5 as a motor supplied frommachine H as a generator. This will avoid the expense of any switchbetween machines I6 and I2. I may thus use a permanent connection I9between such machines and also permanent connections for the directcurrent machines.

In order to give a practicable example, let it be assumed that machineI2 is a 16 pole machine and synchronous machine I3 an 8 pole machine.The synchronous speed of an 8 pole 25 cycle synchronous machine is 375R. P. M. Hence the large set will be brought up to 375 R. P. M. andmachine I3 synchronized and connected with the 25 cycle system II withits field winding energized through rheostat 22 from bus 20. The speedof the main set will thereafter be determined by the frequency of the 25cycle system at 375 R. P. M. with such minor variations from such speedas may occur by slight variations in frequency of the 25 cycle system.The starting motor 28 may now be disconnected. This motor may be a fourpole 25 cycle motor and be started from the 25 cycle system. Also I mayprovide motor IS with an induction starting winding and a pole changingstator winding and use it for starting purposes. The secondary frequencyof the cycle 16 pole machine I2 operating at 375 R. P. M. is 10 cycles.If we make synchronous machine I6 a 2 pole machine, it will need to bebrought to 600 R. P. M. to generate 10 cycles. Hence the auxiliary setis brought to 600 R. P. M. and the field winding of synchronous machineIt energized and its A. C. voltage adjusted so that machine I2 ma besynchronized without shock by closing of the line switch between the 60cycle system and machine I2.

The apparatus is now ready for use as a frequency changer tie. In suchoperation machine I2, although in the form of an induction machine,operates as a double fed synchronous machine with alternating currentexcitation supvwithin desired limits.

2 plied to its secondary by synchronous machine I6. Hence its powerfactor may be adjusted to a high or even leading value by adjusting thedirect current field winding of synchronous machine IB. Likewise thepower factor of synchronous machines I3 and I6 may be controlledbyadjustment of their direct current exciting windings. Thus good powerfactor of all alternating current machines is provided for.

While both machines I2 and I3 operate as ment of the field windings ofthe direct current machines.

If we wish to transmit power from system III to II, machine I2 mustoperate as a motor and machine I3 as a generator. In addition to thepower transferred mechanically through shaft l4 electrical power isgiven out from the secondary of machine I2 to drive auxiliary machine I6as a motor. Machine I1 is driven as a generator and supplies machine Iwhich acts as a motor and assists machine I2 to drive the generator I3.All of the power fed into machine I2 from line ID less the losses in themachines is fed to line II. To effect such operation all that isnecessary is to adjust one or both of the field windings 24 and 25 ofthe direct current machines so that machine I1 operates as a generatorand machine I5 as a motor. To increase the load transfer the current offield winding 25 of machine I'I should be increased or that of fieldwinding 24 of machine I5 decreased or both. To decrease the loadtransfer the direct current field windings are regulated in the reversesense and if this is continued far enough, the transfer of power in allmachines will reverse so as to transfer power from system II to systemI0. When power is being transferred from system II to system I!)machines I3 and I! act as motors and machines I5, I6 and I2 asgenerators.

If desired, automatic control of the power transfer in either directionmay be had by apr paratus such as is shown in Fig. 2. In Fig. 2,represents a contact making wattmeter connected in the leads frommachine I3 to power line I I and which is connected to measure the powerflow from or to such line. It controls a reversible pilot motor 3Iarranged to operate the rheostats 26' and 21 of the field windings 26-and 25. By suitably connecting the wattmeter and adjusting its contactsthe power flow in either direction can be automatically controlledrheosat 26' is cut in, rheostat 21' is out out and vice versa.Similarly, contact making power factor meters may be connected in theoutgoing leads of machines I2 and Ill to automatically control fieldrheostats 23 and 22 to automatically maintain desired power factors.

In designing such a frequency changer set to obtain best economy andoperation consideration should be given to the relative pole number ofmachines I2, I3 and I6 and the frequencies involved. The relativecapacity of the difierent machines for good economy depends upon therelative amount of mechanical and electrical power given out by machineI2 when acting as It will be noted that when 1 a motor or the relativeamount of mechanical and electrical power put into this machine whenacting as a generator. When operating as a motor at full load theelectrical power output from the secondary of machine I2 is proportionalto the rating of the machine times the ratio of secondary to primaryfrequency. Thus, if motor l2 be rated at 20,000 kw. and otherwise ratedas hereinbefore proposed, its full load secondary electrical output willbe /cc 20,000 or 3300 kw. Hence in the example given machines l6, l1 andI5 shouldhave a rating of 3300 kw. Machine I3 should have the samerating as machine 12 if power is to be transferred in both directions.

It will also be generally desirable to select a low secondary frequencyfor machine I2 in order to keep the size of the auxiliary machines aslow as possible, but if we go much below 5 cycles the operation ofsynchronous machine I6 is likely to be unstable.

In order to obtain a good running speed and correspondingly small sizeof the" machines I6 and I], it is desirable to make the pole number ofmachine I6 low, as for example, 2 pole. It is also desirable to connectthe wound secondary induction machine such as I2 to the higher frequencypower system in order to best satisfy the economy conditions explainedabove.

It is, of course, possible to operate the induction machine above itssynchronous speed to ob tain a secondary frequency suiable for stableoperation of synchronous machine I6. If, for instance, in the examplealready given, I change machine I3 from an 8 pole to a 6 pole machine,the speed of the main set will be 500 instead of 375 R. P. M. The 16pole machine I2 will then have to operate above its synchronous speed of450 R. P. M. and will have a secondary frequency of 6% cycles. The 2pole machine I6 will have to operate at the corresponding slower speedof 400 R. P. M. and when machine I2 is acting as a motor machines l6 andI5 will act as generators because with machine I2 operating as a motorabove synchronism, electrical power will have to be put into both itsprimary and secondary windings. Hence machine I2 will have to drive bothmachines I3 and I5 as generators. In general, this will not be aseconomical as the arrangement previously described where machine I2operates below its synchronous speed because where machine I2 operatesbelow synchronous speed the transfer of electrical and mechanical powerthrough machine I2 to or from power line I0 is in the same direction,whereas when machine I2 operates above synchronous speed the reverse istrue.

It will be evident that the apparatus described may be used to supply asystem ID with a regulatable voltage alternating current at a frequencyproportional to the frequency of system II where system I0 has no otherpower supply. The apparatus may be used to supply adjustable frequencypower from machine I3 taking power from power system ID if machine I2 beoperated above its synchronous speed where its operation will be stableand controllable under this condition where machine I3 does not fix thespeed of the main set.

What I claim new and desire to secure by Letters Patent oi the UnitedStates is:

l. A frequency changer comprising a main set having a wound secondaryinduction machine and a synchronous machine with their rotary membersmechanically connected together, auxiliary control apparatus thereforcomprising a synchronous machine and a direct current machine havingtheir rotary members mechanically connected together, the synchronousmachine or said auxiliary apparatus being electrically connected to thesecondary of said induction ma-.v chine, a second direct current machinehaving its rotary member mechanically connected with the rotary membersof the main set and being electrically connected in series with thefirst mentioned direct current machine, a direct current supply for thefield windings of said synchronous and direct current machines and meansfor varying the current in such field windings.

2. A frequency changer comprising a main set having a wound secondaryinduction machine and a synchronous machine with their rotary membersmechanically connected together, auxiliary control apparatus thereforcomprising a synchronous machine and a direct current machine with theirrotary members mechanically connected together, the synchronous machineof said auxiliary apparatus being permanently connected to the secondaryof said induction machine, and a second direct current machine havingits rotary member mechanically connected with the rotary members of themain set and its armature permanently connected in series with thearmature of the first mentioned direct current machine, a separatesource of direct current supply for the field windings of saidsynchronous and direct current machines, and means for individualiyvaryins the currents in said field windings.

3. A frequency changer tie for use between power systems or diil'erentfrequencies comprising an induction machine for connection to the higherfrequency system and a synchronous machine for connection to the lowerfrequency system, said machines having their rotary members on a commonshaft and having a pole num ber relation such that when connected totheir diflerent frequency systems andvoperating at the speed determinedby the synchronous machine the induction machine operates below itssynchronous speed with a secondary frequency of between 5 and 12 cycles,and means for conveying an adjustable amount of power between thesecondary of said induction machine to said shaft comprising anauxiliary synchronous machine electrically connected in series with thesecondary of said induction machine, a direct current machinemechanically connected in driving relation with said auxiliarysynchronous machine and a direct current machine mechanically connectedto said shaft and electrically connected in series with the firstmentioned direct current machine, a separate source of direct currentexcitation for the field windings of the direct current and synchronousmachines and means for adjusting the relative value of the excitationsupplied to the difl'erent field windings.

CHARLES C. CLYMZER.

